Based on the premise that "certain persons with essential hypertension respond differently to a high sodium intake than those who are normotensive or who are non-salt sensitive hypertensives, "this application proposes to test the hypothesis that "salt sensitivity" is not a homogenous group, but that there are several pathologic subsets within this population, and that they can be identified by some biologic markers through their responses to sodium deprivation and loading. Studies will be done by non-invasive techniques in adult normotensives and essential hypertensive patients. Testing this hypothesis requires that measurements of hemodynamic, neural, fluid volume, and humoral factors be made simultaneously, repeatedly and frequently enough to determine the sequence of changes that occur as blood pressure falls in response to salt deprivation and rises with salt loading. Through these studies, we should be able to 1) define "salt sensitivity" more precisely, i.e. whether the factors that mediate the fall in blood pressure with sodium restriction are different from those by which sodium loading causes a rise in blood pressure in the same patient, 2) determine if "salt-sensitive" hypertension is a homogenous group or whether there are pathophysiological subsets within this patient population, and 3) these studies could identify appropriate tests, biological markers and responses that may predict the persons who will become hypertensive later on in life and those hypertensives who would respond best to salt deprivation either through dietary or pharmacologic means. The goal of this study is to provide knowledge of a fundamental nature concerning the characteristics and mechanisms of "salt-sensitive" hypertension in order to improve the diagnosis and treatment of hypertension.